In this section, we will explore the concepts of containers and Docker, which are essential tools for deploying and managing microservices. Containers provide a lightweight, portable, and consistent environment for applications, while Docker is a platform that simplifies the creation, deployment, and management of containers.

• Isolation: Containers encapsulate an application and its dependencies, providing isolation from other applications.
• Lightweight: Unlike virtual machines, containers share the host system's kernel, making them more efficient and faster to start.
• Portability: Containers can run consistently across different environments, from a developer's laptop to production servers.

• Docker Engine: The core component that runs and manages containers.
• Docker Images: Read-only templates used to create containers. An image includes the application code, runtime, libraries, and dependencies.
• Docker Containers: Instances of Docker images that run as isolated processes on the host system.
• Docker Hub: A cloud-based registry service for sharing Docker images.

Follow the installation instructions for your operating system from the official Docker documentation.

A Dockerfile is a text document that contains instructions for building a Docker image.

Navigate to the directory containing the Dockerfile and run the following command:

Run the container using the image you just built:

This command maps port 4000 on your host to port 80 in the container.

Open a web browser and navigate to http://localhost:4000. You should see the output of your application.

1. Create a Simple Web Server:

   • Create a file named app.py with the following content:

   from flask import Flask
   app = Flask(__name__)
   
   @app.route('/')
   def hello():
       return "Hello, World!"
   
   if __name__ == "__main__":
       app.run(host='0.0.0.0', port=80)
   

2. Create a requirements.txt File:

   • Add the following line to a file named requirements.txt:

   Flask==1.1.2
   

3. Create a Dockerfile:

   • Use the Dockerfile provided in the practical example above.

4. Build the Docker Image:

   • Run the command:

   docker build -t simple-web-server .
   

5. Run the Docker Container:

   • Run the command:

   docker run -p 5000:80 simple-web-server
   

6. Verify the Web Server:

   • Open a web browser and navigate to http://localhost:5000. You should see "Hello, World!".

The solution involves following the steps outlined in the exercise. Ensure that each step is completed correctly, and verify the output at each stage.

• Dockerfile Syntax Errors: Ensure that the Dockerfile syntax is correct. Refer to the Dockerfile reference for guidance.
• Port Mapping Issues: Verify that the ports are correctly mapped between the host and the container.
• Dependency Management: Ensure that all dependencies are listed in the requirements.txt file and are correctly installed.

In this section, we covered the basics of containers and Docker, including their key concepts, architecture, and practical usage. We also walked through creating and running a simple Docker container. Understanding these fundamentals is crucial for deploying and managing microservices effectively. In the next section, we will explore orchestration with Kubernetes, which builds on these concepts to manage containerized applications at scale.